Connecting two Solar Regulators

The most common question I get asked on a daily basis is:

"can i connect two solar panels with separate regulators to my one battery bank"

A lot of people when they first start out with their caravan or motor-home mount solar panels on to their roof almost by default. They know they will need solar power and they know that it will help them free camp. However, there are some draw backs with having Solar Panels mounted on to a roof.

If you park in the shade to keep your van cool then the Solar Panels almost become redundant. Even with shade tolerant cells you are still not going to be able to produce enough power to keep the 12v fridge happy.

Nine times out of ten the solar panels are mounted flat which is not the most efficient angle for a solar panels. Mono-crystalline solar panels prefer an angle of about 30 degrees to get the efficiency.

So after splashing out to get solar panels onto the roof and taking off on your first big trip you come back feeling disappointed because your set up didn't quite meet your expectations. Don't beat yourself up too badly about it. Its easily fixed!

The answer is having a combination of both roof mounted panels and portable panels. A portable solar panel enables you to park in the shade and use your portable solar panel's 5 - 10m of cable to put it out in the sun. On top of that your portable solar panel will be set at an angle which will help efficiency and you can move it every hour or so to follow the sun. Great!

But how will two solar panels charge the battery without over charging? Will the two regulators talk to each other? What measures and testing can you do to make sure it all works as it should do? After all you do not want to overcharge your expensive deep cycle batteries now do you?

Here are two options to consider.

Option1: Run both set ups through the same controller. To do this you will need to have a decent level of solar understanding and you will have to apply some modifications. So how would we do that? Lets assume that your solar regulator mounted inside the van for roof mounted solar panels is capable of handling 30amps of solar power. You have 2x 120w panels mounted on the roof which works out as a maximum of 13.4 amps of solar input. This leaves you with 16.6 amps left to fill up with a portable solar panel. Lets now add a 160w portable panel producing 8.89 amps per hour. 13.4a + 8.89a = 22.29 amps per hour maximum. Our 30 amp regulator is more than capable of handling that. Great, but your portable panel has its own regulator. We do not want to run one regulator into another. So now we have to bypass the regulator on the portable solar panel and run directly into the regulator inside the van. How do we do this? We have to install a cable to the solar input section of the regulator inside the van that runs to the outside of the van and fit an Anderson plug to it. We then modify the portable solar panel cabling to bypass the portable solar panel's own regulator and run it into the newly fitted Anderson plug connection. This will now give us a plug and play system that will allow you to charge your batteries easily. Remember though to always make sure that your regulator is able to handle the amperage that both solar set ups are producing other wise you could be left disappointed. I recommend the iTechworld 30a Intelligent Regulator for this kind of set up. You can view more information on that regulator HERE as I mentioned before there is a level of understanding needed to attempt this installation, if this is too hard for you maybe option 2 will be better.

Option 2: Run each setup through its own regulator onto the same battery bank. If you are charging with both regulators at once, keep an eye on your battery(s) to make sure no over charging is taking place. Regulators detect the voltage on your battery and charge it accordingly, so in most instances we've had no issue with having two regulators charging at the same time - as the battery gets full, they both detect it and start to back off. But with this kind of setup you can't take that for granted, do some trial runs and make sure your battery isn't being over/undercharged. If you do discover an issue there is a way to get both regulators singing together.

Disconnect everything

Reconnect both regulators to the battery on their own - no solar panels connected

Leave for 15 minutes

Reconnect solar panels to regulators

This process allows both regulators to detect the battery voltage, type, charge conditions etc without the pressure of applying the charge. When the solar panels are re connected the solar regulators should work more effectively together. Remember to always keep an eye on this set up. A good testing tool for this kind of set up is the iTechworld Amp Meter which will tell you accurately what your solar panels are producing. See HERE.

As always this is just the start of the discussion if you have anything to add leave your comment below.

Hello Ian
Good blog, you confirmed my thoughts.
I had the setup you described, 1 × 120w panel mounted on the roof of the van feeding into a 30 amp reg. But as you say, it wasn’t keeping the charge up to the 2 × 105ah AGM batteries. I was running out of power after a day or 2.
I purchased a portable 200w panel from itech world. When it arrived I faced the issue of having 2 regulators and wasn’t sure if I should use them together. After a little research I did exactly what you describe in option 1. I permanently wired from the van regulator to a weatherproof Anderson plug mounted externally on the van and bypassed the regulator on the portable panel. I have made up several leads of varying lengths with Anderson plugs fitted and can now place my portable panel in the sun while parking the van in the shade.
It works like a dream and there are no more issues with drained batteries.